1. Field of the Invention
This invention relates to a method for the selective dealkylation of alkyl phenols. More particularly, this invention is directed to a catalytic dealkylation process whereby alkyl phenols are reacted with steam in the presence of a catalyst to yield phenol.
2. Description of the Prior Art
Phenol has a wide range of industrial uses, for example, in the production of nylon, plywood, molding compounds, foundry resins, herbicides, surfactants and the like. More particularly, the greatest use for phenol is in the formation of phenolic resins which are primarily consumed in the production of plywood, laminates, and insulation.
The major process for the preparation of phenol involves air oxidation of cumene to yield a hydroperoxide. This hydroperoxide is then subjected to a mild acid treatment to yield phenol and acetone. This process accounts for about 93% of the synthetic production of phenol.
Processes for the dealkylation of alkyl aromatics have acquired significant importance in the petroleum and petrochemical industries. More particularly, these processes have been extensively used in supplementing the benzene demand by dealkylating readily available alkyl substituted benzenes. It is well established that alkyl aromatics, such as toluene, can be dealkylated to lighter aromatics, such as benzene, by reacting such alkyl aromatics with hydrogen in the presence or absence of a catalyst at an elevated pressure and temperature for a controlled length of time. The result of such conditions is the removal of the alkyl group which combines with the hydrogen to yield saturated aliphatic hydrocarbons.
Such hydrodealkylation conditions have been applied to alkyl phenols. However, it has been found that under these conditions, not only the alkyl substituents are removed, the hydroxyl group is also cleaved from the aromatic ring and replaced by hydrogen, thus forming benzene which is undesirable. The cleaved hydroxyl group also combines with the hydrogen to form water. Consequently, alkyl phenols, when subjected to hydrodealkylation conditions, yield, in addition to water, alkyl aromatics and benzene instead of phenol. Furthermore, in excessive amount of hydrogen is consumed.
As a result of the energy crisis, it is becoming increasingly apparent that the cost of hydrogen production from once non-expensive hydrocarbon feedstocks is rapidly increasing. It follows that the cost of hydrogen consuming processes, such as hydrodealkylation, also increases significantly. Thus, interest in processes using steam in place of hydrogen for reforming petroleum feedstocks is increasing. Steam is also preferred because it is readily available and yields, on reaction, readily recoverable and valuable hydrogen. Furthermore, catalytic steam processes are preferable because the presence of the catalyst lowers the energy of activation of the reaction, and, therefore, requires less severe reaction conditions.
The catalytic steam dealkylation of toluene and other benzene homologues has been extensively patented and reported in the literature. Typical catalyst compositions include zeolites or amorphous inorganic oxides, such as silica, alumina, silica-alumina, and the like, in conjunction with other metals or metal oxides. These types of catalysts have shown remarkable initial activity when compared to non-catalytic processes under the same conditions. For the steam dealkylation of toluene over gamma-alumina supported noble metals, benzene selectivity in the range of from 60 to about 98 mole % has been reported. Unfortunately, this type of catalyst undergoes rapid deactivation which appears to be due to the formation of coke on the surface of the catalyst, thus rendering the catalytic surface relatively inaccessible to further reaction. As time elapses, the activity of the catalyst declines to such a low level that the process must be temporarily halted to regenerate or replace the catalyst. As a result, the deactivation of the catalyst makes the catalytic steam dealkylation process only marginally effective as a commercial process.
Thus, it is apparent that there is a need for a process for dealkylating alkyl phenols, such process being capable of commercial application as well as economically feasible.
It has been found by the present invention that the alkyl group in an alkylated phenol may be removed by reacting the alkylated phenol with steam in the presence of a catalyst which comprises a hydrous carrier, a deactivation suppressor, and a promoter.
It has also been discovered that by mixing the alkylated phenol feed with an alkali metal salt, the rate of catalyst deactivation is reduced and also the selectivity for phenol is enhanced.